1. Field of the Invention
The present invention relates to a metal vessels used, for example, used as an ice box, a thermos bottle, vacuum thermos cookware, heat-retaining electrical pot, and heat-retaining tank, and a method for fabrication of the same.
This application is based on patent application Nos. Hei 10-36434 and Hei 10-36435, filed in Japan, the content of which is incorporated herein by reference.
2. Description of Related Art
Conventionally, metal tubular vessels having a bottom are fabricated. These vessels are, for example, double-layered vessels comprising an integral inner vessel and outer vessel made using stainless steel, etc., or double-walled vacuum metal vessels having an inner and outer vessel with a vacuum therebetween providing superior heat-retention, or double-walled metal vessels with air maintained between the inner and outer vessels. In addition, these are used as vessels having a simple single layer metal, such as for flasks and table pots.
An example one such conventional metal vessel has an opening on the upper part, and comprises a shell member with a diameter larger than the diameter of the opening part, and a bottom member. A specific example is the metal vessel 101A, as shown in FIG. 15, wherein a bottom member 103 has an external diameter approximately the same as the shell member 102 and formed in a vessel shape with a bottom being abutted to the shell member 102, welded, and made integral.
In addition, as shown in FIG. 17, another example is the metal vessel 101C, wherein a bottom member 105 has an external diameter approximately the same as inner diameter of the shell member 102, has the shape of an inverted dish which protrudes inward into the vessel, is inserted into the shell member 102, and whose end surface is welded and made integral with the end surface of the shell member 102. Furthermore, as shown in FIG. 16, there is a metal vessel 101B wherein the bottom member 104 having an external diameter almost the same as external diameter of the shell member 102 is abutted with the end surface of the shell member 102, welded, and made integral.
These metal vessels are conventionally manufactured in the following manner.
After stamping a flat metal plate into the desired shape, by rolling and welding the edges, a cylinder (straight tube) is formed with both ends opening at about the same diameter, and then after forming a truncated cone whose openings at either end have different diameters (a tapered tube), a shell member is formed by expanding and reducing a shell by pressing or spinning. Then, a cup-shape is formed from a flat plate by pressing, and a bottom member formed by cutting off the flange thereof is welded to this shell member, producing a metal vessel.
In addition, after stamping a metal flat plate into the desired shape, it is rolled, and formed into a cylinder by welding the edges, and then, in the same manner, after welding the bottom member formed into a cup-shape by pressing, etc., to the cylinder, a shell member is formed by reducing the shell by spinning, etc., producing a metal vessel.
Furthermore, a different method for fabricating metal vessels is disclosed in Japanese Patent Application, Second Publication, No. Hei 7-41007. Therein, after they are welded and made integral, a shell member and the bottom member are expanded by a hydraulic bulge processing. If a radially expanding method using hydraulic bulge is used, a metal vessel having a widthwise cross-sectional shape other than a cylindrical shape, such as an elliptical shape or polygonal shape, can be obtained.
However, in the fabrication of metal vessels using conventional pressing and spinning, as a whole, much time is consumed because generally multiple expanding steps by the pressing and ironing of the rollers is carried out, as the processing time passes making cross-over time for transiting from one step to another is necessary.
In addition, in these processes the widthwise cross-sectional shape of the product is limited to a round shape because welding is difficult if the widthwise cross-sectional shape is not cylindrical. Furthermore, in order to make local deformations, there is the problem that defects such as fractures are produced during the formation. In addition, because of thinning of the formed parts, there is the problem that the strength of endurance when dropped, etc., is weakened.
Furthermore, when a metal vessel fabricated in this manner is to be used as the inner vessel of a double-layered vacuum vessel and metal plating is applied to the outer surface of the shell, there is the possibility of deterioration of the adhesion of the plating due to this unevenness, and thus fine unevenness and formation defects may be produced on the surface of steel processed by spinning and pressing.
In addition, the fabrication method using hydraulic bulge processing has the advantages of decreasing the number of steps in comparison to pressing and spinning, and decreasing the amount of processing time. However, because a deforming force is also used at the welded part, fractures may be produced in the welded part, and the product yield is lowered. For example, the shear force at the welded part when the total circumference of the shell member-bottom member is increased during the expansion of the welded part. In addition, in order to decrease the production of fractures, it is necessary to carry out pressure filling slowly. This decreases the speed of the expansion, which makes it impossible to carry out the hydraulic bulge process in the originally desired time, and further makes it impossible to sufficiently exhibit the characteristics of hydraulic bulge processing.
In addition, among the conventional metal vessels shown in the above-mentioned FIG. 15.about.FIG. 17, in the metal vessel 101A having the structure shown in FIG. 15, a mis-aligning in the welding between the shell member 102 and the bottom member 103 is easily produced, causing a deterioration in appearance. In addition, when the plate of both members is thin, there is a concern that defective welds will be produced. Furthermore, there are the problems that it soils easily because the surface of the welded part 106 is not smooth, and it is difficult to clean with a sponge or scrubbing brush because the inner diameter of the welded part is larger than the diameter of the opening.
In addition, when fabricating the vessel, there was no freedom in the shape because it is necessary to press down with a jig, etc., during welding, and because the shape of the shell is round and requires a straight part. Additionally, because the bottom member 103 is weak, there are the problems that it dents easily, and it is unstable when placed on a flat surface.
In addition, because the metal vessel 101B having the structure shown in FIG. 16 produces a gap in the welded part 106 in the interior of the vessel, there are the problems that it is easy for soilage to accumulate, and it is difficult to wash. Because of this, there is the concern that the soilage in the gap may decay, and thus these are not suitable in particular as food containers. In addition, crevice corrosion may be produced in the welded part 106, and thus these are not suitable for containing highly corrosive substances.
Furthermore, if the shell member 102 of the metal vessel 101C having the structure shown in FIG. 17 is not cylindrical, welding is very troublesome, and thus the shape of the shell member 102 cannot be selected freely. In addition, the bottom member 105 is weak, and when a solid substance such as ice is dropped into the opening, it can be easily deformed and dented.
Furthermore, because the inner diameter of the welded part is larger than the opening, there is the problem that the accumulated soilage in the welded part 106 cannot easily be cleaned with a sponge or scrubbing brush